Signaling system for communication channels with pulsating currents over tube repeating amplifiers



March 25, 1941- K H. THUNELL ETAL PULSATING CURRENTS OVER SIGNALINGSYSTEM FOR COMMUNICATION CHANNELS WITH -TUBE REPEATING AMPLIFIERS FiledAug. 17, 1939 2 Sheets-Sheet 1 I LC Karl Hurp hq 'S'mn Davue] V\ Yen@rHQY'YS Ehas C uasso March 25, 1941. H, THUNELL ETAL 2,236,225

SIGNALING SYSTEM FOR COMMUNICATION CHANNELS WITH PULSATING CURRENTS OVERTUBE REPEATING AMPLIFIERS FilQd Aug. 17, 1939 2 Sh'eets-Sheet 2 I I I lI I I l I l l I I I I l I I I l I I l I I 8+ Dawn's vi e \NVENTOBS 1m)PCFT y,

Patented Mar. 25, 1941 UNITED STATES SIGNALING SYSTEM FOR COMMUNICATIONCHANNELS WITH P'ULSATING CURRENTS OVER- TUBE- REPEATING AIVIPLIFIERSKarl Harry Thunell, Sten Daniel Vigren, and Per Harry Elias Claesson,Stockholm, Sweden Application August 17, 1939,'Serial No. 290,570

Claims. (01. 179-4) The present invention relates to new and usefulimprovements in the transmission of pulsating direct currents inone orboth directions over (inductively connected) electric circuits orchannels comprising vacuum or other tube repeating amplifiers throughwhich the signals must pass.

The invention refers particularly to circuits and channels in telephone,telegraph, carrier and radio signaling systems, preferably of the type10 needing trunk facilities for two-way trafiic between exchanges orstations, although the invention can be used also for transmission inone direction only.

The invention is particularly suitable for the transmission of signalsover long distance lines of two or four wires with or without carrierchan nels, over radio carrier channels and the like. The signalingsystem enables a station or an operator of a certain telephone exchangeto dial the number desired of an automatic exchange of a distant cityand on the same time receiving all necessary traffic signals in theproper exchange or station, such as busy, clearing, time-measuring,debiting and like signals.

The present invention will greatly facilitate the inter-city and longdistance traffic in a simple and cheap way, whereby the distant andeventually the originating long distance operators can be eliminated.

Also on channels where the long distance operators are still maintained,the new signal system can be used for calling, clearing and othersignals.

The invention is also suitable for telegraph and other signals which canbe transmitted over special carriers by Wire or radio channels.

Heretofore different signal systems have been used for the transmissionof signals over communication circuits, depending upon the distancebetween the two stations.

Signals based upon the use of direct currents are generally used incases where it is desired to have the signals continue to indicate thecondition of a connection throughout the conversation, for example,since the direct current can continue to flow over a continuous wirecircuit simultaneously with the Voice currents during conversationwithout interference. The most extensive use of this type of signalinghas been made for the short local circuits.

In the early days the method of operation of long toll circuits wasgenerally such that no signal was required over the toll circuit duringthe conversation period but only before and after the conversation andfor such signals alternating currents of, for example, 16, 20, 50, 60and 135 cycles Were used.

'With the further development of long toll circuits with many vacuumtube repeaters at intermediate points and also with the development ofcarrier telephone systems, the low frequencies of 16 2 0, 50 and 60cycles could not pass the repeaters and the satisfactory transmission of135 cycle current from one end of the circuit to the other became moredifiicult.

Later on interrupted voice frequency currents of 500 cycles in Europeand 1000* cycles in U. S. A. were introduced assignaling means. Withsuch a system 'the signaling current uses the same transmission path asthe voice currents, but the system is designed to discriminate betweenthe voice and signaling currents at the beginning and at the end of thecircuit by means of complicated equipments. The 500-cycle and theIOOO-cycle systems are now in use for the majority of circuits over 200to 300 kilometers of length.

With the recent development of automatic telephony it became desirableto reach a station in a distant automatic exchange by causing theoriginating operator to dial the called number directly over a long tollline without the assistance of an inward operator at the called place.For said purpose interrupted voice frequency currents of differentfrequencies or of different lengths have been used for difierentsignals. If different frequencies are used, different voice frequencytransmitters and receivers have to be used for each kind of signal andif the same frequency is used, but of different length, complicatedrelaysets are resorted to. Both methods are expensive and not entirelysatisfactory.

The present invention eliminates all the above mentioned difiicultiesand offers a simple solution of transmitting pulsating half-cyclecurrents of, for example, 10 cycles or of the same kind as those emittedby the dial of an automatic telephone station over communicationchannels of any length provided with ordinary voice and/or carrierrepeaters.

Our copending U. S. application Ser. No. 289,158, filed November 5,1938, described a signaling system for the simultaneous transmission ofsignals in both directions over a trunk line by means of pulsatingcurrents of any desired sequence of polarity between two stations, eachthereof comprising a direct current source, transmitting and receivingmeans, connecting means permanently and inductively connecting saidstations and said transmitting and receiving means to said trunk line,balancing means associated with said transmitting, receiving andconnecting means, said balancing and connecting means be ing of such amagnetic constitution and electricity so connected that their magneticand electrical characteristics remain substantially constant at anynormally transmitted current magnitude at any of the stations.

Said invention, however, refers only to lines inductively connected andprovided with means,

whereby it is possible to transmit heavy pulsating currents of greatvoltage and amplitude over the line without changing the magnetic andelectrical characteristics of the special signal transformers neededaccording to the invention, covered in said application, as otherwisethe balance between sending and receiving side on the same station wouldbe disturbed.

The present invention refers generally to a transmitting system for thetransmission of pulsating half-cycle direct signal currents of anysequence of polarity and of about the same magnitude as that of voicefrequency currents to be transmitted over a communication channelbetween two stations, transmitting means connected to the transmittingchannel at one station and at the other station receiving meansconnected to said channel, said receiving means comprising repeating andamplifying electron tubes in series with said channel, means forseparating said pulsating half-cycle signal currents from dampened orcontinuous wave currents or voice frequency currents transmitted oversaid channel, and an operating device responsive to any polarity of saidhalf-cycle signal currents.

The present invention refers particularly to a transmitting systemcomprising the transmission of signals in both directions over a two-waycommunication channel system, provided with tube repeating amplifiers bymeans of pulsating halfcycle signal currents of any desired sequence ofpolarity, in which there are two stations, each thereof comprising adirect current source, signal transmitting and receiving means,connecting means permanently and inductively connecting said stations tosaid communication system, balancing means associated with saidtransmitting, receiving and connection means, said receiving meanscomprising a tube repeating amplifier and means for separating saidpulsating half-cycle signal currents from voice frequency currents, andan operating device responsive to any sequence of polarity of saidhalf-cycle signal currents.

No specially constructed transformers are needed and the signal impulsescan be repeated and/or amplified in vacuum tube repeaters or similardevices which are needed according to this invention, particularly atthe receiving end to discriminate the half-cycle pulsating currents fromvoice frequency currents and to amplify said impulses in order tooperate a polarized relay or other current-direction discriminatingdevice.

The invention can be used for transmitting and receiving in onedirection only, when there is a need of transmitting orders, reports orthe like to one or a plurality of places, where messages are receivedonly, for example in the transmission of telegraph or code signals overtelegraph, telephone, carrier or radio net-works, such as used frompolice headquarters to police stations and radio-patrol cars, thetransmission of stock-exchange rates and the like.

According to a preferred feature of the invention the half-cycle signalcurrents, of for example dial-impulses, are limited to about the sameduration as half a cycle within the lower part of a voice-frequencyrange to be transmitted over the said communication channel system, inwhich case no change is needed in filters or in other equipment ofexisting communication channels.

According to another feature of the invention and particularly whencarrier and radio channels are used, half-cycle signal currents offairly great duration, for example of about 10 cycles per second from adial, can be modulated directly on the carrier. In this case themodulation filter curve must be steeper and broader than now generallyused for only letting through the voice frequency band.

The invention is further described and explained in connection with theaccompanying drawings of which:

Fig. 1 represents a simplified diagram of two exchanges or stationsinductively interconnected by a four-wire two-way circuit using twooneway transmission channels, eventually provided with carriers and tuberepeating amplifiers.

Fig. 2 represents a positive half-cycle signal current to be transmittedover the system.

Fig. 3 represents a dampened wave train of impulses.

Fig. 4 represents a negative and a positive halfcycle of signalcurrents, each one of about the same duration as half a cycle within thelower part of a voice frequency range to be transmitted over acommunication channel.

Fig. 5 is a diagram showing a positive halfcycle signal current as thatone shown in Fig. 2 and a dampened wave train similar to that shown inFig. 3 arriving close together to discriminating means todiscriminatebetween the two kinds of impulses.

Fig. 6 represents in a simplified diagram the simplest form oftransmitting and receiving means according to the invention.

Fig, 7 represents a simplified diagram of two stations or exchangesinductively interconnected by a two-wire two-way circuit, eventuallyprovided with two-way tube repeaters on the line.

Fig. 8 represents a simplified diagram of a terminal exchange or stationof a two-way radio communication, using two one-way carrier channels,eventually with low-pass filters for the transmission oflow-frequencyhalf-cycles of long duration modulated on a carrier wave.

Fig. 9 represents a filter for the upper side band which apart from thevoice frequency band allows half-cycles of long duration and lowfrequencies to be modulated on a carrier wave.

The inventive idea can, of course, be varied in a great number of ways,depending upon the transmission system in which the invention shall beused and also depending upon the type of signals that shall betransmitted.

In Fig. 1 A and B are two terminal telephone exchanges united by afour-wire long distance toll line with or without carrier and/orrepeaters on the line proper. The talking circuit a--b in the exchange Ais inductively connected to the line channel circuit 'lll2 and '|314 bymeans of the filter network 15 and the hybrid coil 15. The signaltransmitting means is inductively connected to the one-way line channel'Il-l'2 by means of the signal transformer 11, while the receiving meansare inductively connected to the other one-way line channel l3'l4 bymeans of the signal transformer I8. The object of network 15 is to actas an amplitude limiting device of the talking currents and also totransform any individual, undesirable half cycles that might arrive overthe talking circuit during a conversation from the exchange side intodampened waves, before being transmitted to the line circuit. 19 is abalancing network. A! is the impulse transmitting relay with windings I3and I4, directly or indirectly controlled by a subscriber's dial or by asimilar device. 80 is a discriminating storage and receiving device forthe pulsating currents shown in detail on station B. 8| is a transformerfor amplifying the received pulsating half-cycle currents 82 is a biasedpolarized relay with armature 44 and break contact 45. I5 is a batterysource on station A. I6 and H are resistances, I8 is a condenser. I9 isa preferably variable resistance to cause heavily dampened oscillations,when the condenser |8 is discharged. 20 is a potentiometer to serve asan amplitude limiting device for the half-cycle currents to betransmitted over the line '||-|2. 2| is a modulating device, 22 a bandfilter, 23 repeaters on the line. 24 is a band filter and 25 ademodulating device on station B for the communication channel from A toB.

On station B 26 and 21 are tube amplifiers, connected in push-pull. 28is a filament battery, 29 a grid battery and 32 a plate battery. 30 and3| are half-windings of secondary winding of transformers 18'. 33--34 isa potentiometer, the mid-point of which is connected to the platebattery 32. 35 is a storage device in the form of a condenser for thehalf-cycle signal currents. 36 is an amplifier with filament battery 31,grid battery 38 and plate battery 39. 82' is a polarized relay with adoubly biased armature 43 and make contacts 4| and 42. Other partsonstation B are similarly marked as on station A.

On station A the following relays are used for the transmission of thesignal impulses: Al to A4 inclusive.

On station B the following relays are used for receiving signals from Aand for transmitting signals from B to A: BI to BB inclusive. The relaycontacts on each relay are numbered progressively with the same numbersfor the sake of simplicity. To distinguish, for example, contact spring5 on relay AI, said spring is designated 5Al.

In Fig. 2 is shown a signal positive half-cycle c and a heavily dampenednegative half-cycle d. As is well known it is very difficult to obtainjust one single half-cycle, when opening or closing a signal circuit, asseveral impulses more or less dampened are obtained like those shown inFig. 3. The signal half-cycle currents are heavily dampened in thesending circuit so that the difference in amplitude, for instance,between the first positive and the second negative half-cycle is verygreat.

A less dampened wave train is shown in Fig. 3 in which the differencesin amplitude between a positive e and a negative consecutive 1 halfcycleis very small.

Figs. 4 and 5 explain one of the basic ideas of the invention andparticularly how the signal receiving device can discriminate betweenthe half-cycle signal currents proper and a dampened or continuous wavetrain as shown by the dotted line in Fig. 4 or in Fig. 3.

If the amplitude of a signal operating halfcycle is more or less thesame as the amplitude of ordinary voice currents as shown in Fig. 4, theprinciple of the discriminating device according to the invention isshown in Fig. 5.

Fig. 5 represents the grid-plate-current characteristic curves of tubes26 and 21 of the pushpull amplifier, shown in Fig. 1. A wave trainarriving over the transformer 18' is shown on the negative ordinateshown in Fig. 5 and is composed of a positive half-cycle signal current0 and a heavily dampened tail-half-cycle :1. Immediately following is asemi-dampened train of impulses ef-gh of the kind shown in Fig. 3.

Upon the arrival of positive and negative halfcycles the condenser 35(Fig. 1) is alternatively charged and discharged over the potentiometer3334, and simultaneously increases or decreases the grid potential ofthe amplifying tube 36 which controls the polarized relay 82.

Fig. 5 thus shows that if about positive and negative half-cycles ofequal or slightly varying amplitude arrive, the rest charge of thecondenser 35 will be zero and accordingly will not cause any change inthe grid voltage of amplifying tube 36 or to the polarized relay 82. Itcan thus be observed from Fig. 5 that the amplified negative half-cyclesf and h will neutralize the amplified positive half-cycles e and g.

It is preferred that the negative grid voltage of the push-pull deviceis sufficiently great so that the plate current ordinarily remains zero,because in such a case the positive and negative operating half-cycleswill be amplified on the straight parts of the grid-plate-currentcharacteristic curve. Due to the low amplitude of the tail negativehalf-cycle d following upon an operating half-cycle c saidtail-half-cycle will hardly be amplified at all because corresponding tothe lowest part of the amplifying characteristic curve. The same is thecase with the rest charges of the condenser 35 which are due to smalldifferences of amplitude of consecutive half-cycles of continuous wavetrains. If the consecutive half-cycles of, for example, an undampenedwave train are all alike, no charge will be stored in the condenser 35.From Fig. 5 we find that of the six half-cycles c-h only the operatingsignal-half-cycle c is stored in condenser 35.

The general operation of the transmission of signal half-cycles over thefour-wire carrier channel system shown in Fig. 1 is the following: Acalling station connected to exchange A, desiring connection over a longdistance toll line to exchange B, obtains after certain connectingoperations over known circuit arrangements, not shown in the drawing,connection to the repeating relay AI, which is energized when thereceiver is off the hook. Relay A2 is thereby energized and its contactsand 2 are closed, whereinduced a voltage, causing a signal currentimpulse in series with the line '||-|2. If a carrier is used, the signalcurrents are modulated together with the voice frequency currents comingover the hybrid coil 16 in modulator 2|. If the signal half-cyclecurrents have about the same duration as half a cycle of the lower partof the voice frequency, ordinary band filter 22 is used to eliminate theupper or lower side band of the carrier wave.

If the half-cycles transmitted are of long duration, for example of thekind produced in an ordinary dial of about 10 complete cycles or 20half-cycles per second after having passed the signal transformer H, theband filters 22 and 24 must be made wider and sharper than thoseordinarily used so that the signal impulses can be modulated onthecarrier wave in the same way as the voice frequency currents. Such aband filter characteristic curve is shown in Fig.-

9. In said way the low frequency signal impulses modulated on thecarrier will pass the ordinary line repeaters 23 in the same way as thevoice frequency currents do. The signal currents pass on station B inseries with the primary winding of signal transformer 18'. If thearriving halfcycle signal current is positive, a current impulse isinduced in, for example, the upper half-winding 3| of the secondary oftransformer 18'. This half-cycle current is amplified in amplifier 26over resistance 33, whereby the condenser 35 is simultaneously chargedin series with resistance 34. By choosing the magnitude of theresistances of potentiometer 33-34 the condenser 35 can be made to becharged or discharged more or less slowly over either of saidresistances, thereby increasing the duration of the posterior dischargeof the signal half-cycle energy stored in the condenser 35.

The object of the amplifier 36 is to increase the amplitude of thehalf-cycle signal current stored in condenser 35 when afterwards beingdischarged over the grid circuit of amplifier 35. If the condenser 35 ispositively or negatively charged the grid voltage of amplifier 36 isinfluenced in one or the other direction causing positive or negativecurrent impulses in the primary and secondary of transformer 3i and thearmature 43 of the polarized doubly biased relay 32 is moved to makemomentary contact with contact 4! or contact 42.

Instead of a polarized relay other devices responding to positive ornegative currents can be used, for example two ordinary relays,connected in parallel, each one with a rectifier in series and connectedin opposite directions.

If a negative half-cycle is received at line signal transformer 18, itis passing through its lower secondary winding an and is amplified inamplifier 2'! and in the same way as previously described the negativehalf-cycle is amplified and received at relay 82'.

If, for example, a positive half-cycle has been received by polarizedrelay 82', the armature 43 makes contact with contact 4|, closing thefollowing circuit: Ground, armature 43, contact 4|, l-2B5, relay B5,battery I. Relay B5 is energized closing contacts 3-4, 1-8, 9-H), Il-l2and breaking contacts I-2, 5-6. Relay B5 received holding current overthe following circuit: Battery 15', winding of relay B5, 3-4B5, 2-lB4,ground. On account of this holding circuit relay B5 remains energizedalso after the armature 43 of polarized relay 82' returns to normalposition. When relay B5 was energized relays B5 and B3 were energized.B3 was energized over the following circuit: Ground, 8-1B5, winding ofslow acting relay B6, battery l5. B3 was energized over the followingcircuit: Ground, iii-9B5, winding of relay B3, resistance l5, batteryI5, as soon as armature 43 of polarized relay 32' returns to normalposition. When relay B3 is energized it closes its contacts 2-3 andprepares the circuit for relay B2, if the next halfcycle received alsoshould be positive.

If now a negative halfcycle, however, is transmitted at A by releasingrelay Ai, contacts l-ZAI are closed. Condenser i8 is thereby chargedwith a potential opposite to the previous charge. In similar manner asabove described this negative half-cycle is transmitted at A andreceived and stored at B by condenser 35, which now obtains a charge ofa potential opposite to that previously obtained. When condenser 35discharges through potentiometer 33-34 the impulse magnified byamplifier 33 and transformer 8! is received by polarized relay 32',whereby armature 43 makes contact with contact 42. Relay B4 is therebyenergized according to the following circuit: Ground, contact 43-42,winding of relay B4, battery l5. Contact l-2B4 is opened, interruptingholding current of relay B5, which is ole-energized and opens itscontacts H-IZBS.

If contact H-iZBS is connected to a selector controlling circuit onstation B, a positive and a negative half-cycle signal currenttransmitted at station A is received at station B and transformed intoselecting impulses by closing and opening a contact such as ll-I2B5.

If instead of transmitting positive and negative half-cycles as abovedescribed, two consecutive positive half-cycles shall be transmitted,such a transmission takes place in the following way: Previouslycondenser it! had been positively charged, when 2-3Al was closed upon Alenergizing its armature and a positive half-cycle current wastransmitted over the line. Current is then continuing to flow over thefollowing circuit: Battery l5, primary winding of transformer H,resistance l9, 2-3Al, resistance IT, ground. The condenser I8 is therebykept charged over the following circuit: Battery 15, primary winding oftransformer T1, 3-2A4, condenser l8, 3-2Al, resistance l1, ground.

If now a second positive half-cycle current shall be transmitted, relayA4 is caused to be energized in known way, thereby breaking contact3-2A4 and closing contact l-2A4. Condenser i8 is then discharged throughresistance 46.

When relay A4 is de-energized, contact 2-3A4 is again closed andcondenser 18 is again positively charged according to the followingcircuit: Ground, 3-2Al, condenser l8, 3-2A4, primary winding oftransformer H, battery [5. The current previously flowing through thesame winding is increased as soon as the condenser I8 is again connectedin the circuit, parallel to the variable resistance 19, which, ofcourse, is of fairly great magnitude. A half-cycle current of the samedirection as the previous one is then generated in the secondary windingof transformer 11. It is understood that the closing of contacts l-2A4takes place before contacts 2-3A4 are opened so that no change in thecurrent passing through the primary winding of transformer H, takesplace, when A4 is energized.

When such a second consecutive positive halfcycle signal current arrivesat station B, armature 43 is again caused to make contact with contact45, now closing the following circuit: Ground, contacts 43-4! ofpolarized relay 82, 2-333 which was energized before, relay B2, batteryl5. Relay B2 closes its contact I-2 and connects ground to a wire gwhich can be used for eventually breaking a local connection of a partyfor which a long-distance toll call may be waiting.

Signals in the direction from B to A can be sent in similar manner tothat above described. Thus can on station A a signal be receivedindicating when station 13 answers, or when the conversation isfinished, a connection counter and time measuring device can be made tooper- F ceived at A by polarized relay 82, the biased armature of whichtemporarily breaks the contact 44-45 of a, control circuit on station A.

Relays A3 and B1 are used to eventually disconnect the talking circuitsfrom the signaling circuits, while signals are being transmitted.

In Fig. 6 the transmission and reception of half-cycle signals overamplifiers is shown in the simplest form. To the left. is showntransmitting means, equal to those shown in Fig. 1. The line can bedirect or provided with amplifiers. To the right is shown a simplifiedsignal receiving device similar to that shown in Fig. 1, but instead ofpotentiometer 33-44, the primary 41-48 of transformer BI is used. Theplate battery 32 is connected to the center point of said primary. Theenergy storing device or the condenser 35' is connected in series with aresistance 5B in parallel to the secondary 49 and in parallel to thepolarized relay 82'. The extra amplification tube 36 shown in Fig. 1 isomitted here.

The transmission and reception of signals in Fig. 6 is very similar tothat described in Fig. 1.

Fig. 7 shows a two-wire connection between two exchanges, provided withamplifiers and echo-suppressers on each station. The line can be director provided with two-way repeaters in known manner. Transmission andreception can be made in both directions. Reference numbers in Fig. '7refer to same devices as shown in Fig. 6 or Fig. 1. 5i and 52, 5! and 52are hybrid coils in respective station amplifiers. 53 and 53 are linebalancing net-works. l9 and F9 are station balancing net-works. 5d and55, 54' and 55 are sending and receiving voice frequency amplifiersrespectively. 56 and 56' are echosuppressers which might be needed onlong two- Wire circuits with many two-way repeaters in series.

In Fig. 8 is shown a sending and receiving device on a station for atwo-way radio communication channel. Sending and receiving devices aresimilar to those previously shown. Instead of a physical line a radiochannel system is used in which 51 is an amplifier, 58 a modulator, 59oscillator and amplifier, Bil an amplifier and 6| the sending antenna.62 is the receiving antenna, 63 is the radio receiving and demodulatingdevices, M is a low-pass filter, which is used if the half-cycle signalimpulses are of low frequency and long duration. 65 is an amplifyingdevice and I2 a polarized relay to receive the demodulated half-cyclesignals.

The distant station shall, of course, be similarly equipped if a two-waycommunication is desired.

The invention is not limited to the described figures which only show afew applications of the general and special forms of the invention andit is clearly understood that the general inventive ideas can be used inany combination, where signal half-cycle currents can be transmittedthrough an amplifier with or without a filtering net-work, be it thatthe half-cycles are of a duration equal to those within the voicefrequency range or below or above said range.

In Fig. 9 is shown a filtering curve 66, which can be used in carrierchannel systems over line wires. The curve 66 indicates that the upperside band is passed through the filter which is wide enough to letthrough both the carrier frequency fm with the upper parts of the voiceand signal frequency bands, 61 and 68 respectively.

If frequency modulation is used or in radio communication both the lower(dotted parts in the figure) and the upper side bands are passed throughthe filter, 6B and 69 respectively.

What we claim is:

1. In a transmitting system comprising the transmission of pulsatinghalf-cycle direct signal currents of any sequence of polarity in bothdirections and of about the same magnitude as that of Voice frequencycurrents to be transmitted over a twoway communication channel,repeating electron tubes connected in series with said channel, twostations each thereof comprising a direct current source, signaltransmitting and. receiving means, connecting means permanently andinductively connecting said stations to said communication channel,balancing means associated with said transmitting, receiving andconnecting means, said receiving means comprising means for separatingsaid pulsating half-cycle signal currents from voice frequency currents,and an operating device responsive to any polarity of said half-cyclesignal currents.

2. In a transmitting system comprising the transmission of pulsatinghalf-cycle direct signal currents of any sequence of polarity in bothdirections and of about the same magnitude as that of voice frequencycurrents to be transmitted over a two-way communication channel,repeating electron tubes connected in series with said channel, twostations, each thereof compris ing a direct current source, signaltransmitting and receiving means, connecting means permanently andinductively connecting said stations tosaid communication channel,balancing means associated with said transmitting, receiving andconnecting means, said repeating electron tubes associated with saidreceiving means, the latter comprising means for separating saidpulsating half-cycle signal currents from voice frequency currents, saidseparating means comprising a condenser for storing the energy of saidpulsating half-cycle signal currents, and an operating device responsiveto any polarity of said halfcycle signal currents.

3. In a transmitting system comprising the transmission of pulsatinghalf-cycle direct signal currents of any sequence of polarity in bothdirections and of about the same magnitude as that of voice frequencycurrents to be transmitted over a four-wire circuit comprising twooneway communication channels, repeating electron tubes connected in.series with each one-way communication channel, two stations, eachthereof comprising a direct current source, signal transmitting andreceiving means, connecting means permanently and inductively connectingsaid stations to said communication channel, balancing means associatedwith said transmitting, receiving and connecting means, said receivingmeans comprising an electron tube amplifier and means for separatingsaid pulsating half-cycle signal currents from voice frequency currents,said separating means comprising a condenser for storing the energy ofsaid pulsating half cycle signal currents and an operating deviceresponsive to any polarity of said halfcycle signal currents.

4. In a transmitting system comprising the transmission of pulsatinghalf-cycle direct signal currents of any sequence of polarity in bothdirections and of about the same magnitude as that of voice frequencycurrents to be transmitted over a physical circuit comprising equipmentfor two carrier communication channels to be operated in oppositedirections, repeating electron tubes connected in series with saidphysical circuits, two stations, each thereof comprising a directcurrent source, transmitting and receiving means, connecting meanspermanently and inductively connecting said stations to said circuit andchannels, balancing means associated with said transmitting, receivingand connecting means, a carrier current generating source, modulating,demodulating and filtering means associated with said carrier channelsto modulate and demodulate the half-cycle signal and voice frequencycurrents with respect to carrier waves to be transmitted over saidchannels, said receiving means comprising means for separating saiddemodulated pulsating half-signal currents from voice frequencycurrents, said separating means comprising a condenser for storing theenergy of said pulsating half-cycle signal currents and an operatingdevice responsive to any polarity of said half-cycle signal currents.

5. In a transmitting system comprising the transmission of pulsatinghalf-cycle direct signa1 currents of any sequence of polarity in bothdirections and of about the same magnitude as that of voice frequencycurrents to be transmitted over two radio communication carrier channelsto be operated in opposite directions, two stations, each thereofcomprising a direct current source, a carrier generating source, trans-:mitting and receiving means, connecting means permanently andinductively connecting said transmitting and receiving means to the tworadio communication carrier channels, balancing means associated withsaid transmitting, receiving and connecting means, modulatingdemodulating and filtering means to modulate and demodulate thehalf-cycle signal currents with respect to the respective radio carriersto be transmitted, said receiving means comprising means for separatingsaid demodulated pulsating halfcycle signal currents from voicefrequency currents, said separating means comprising a condenser forstoring the energy of said pulsating half-cycle signal currents, and anoperating device responsive to any polarity of said half-cycle signalcurrents.

6. In a transmitting system comprising the transmission of pulsatinghalf-cycle direct signal currents of any sequence of polarity and ofabout the same magnitude as that of voice frequency currents to betransmitted over a communication channel, two stations, a direct currentsource at each station, at one station transmitting means connected tothe transmitting channel and at the other stat-ion receiving meansconnected to said channel, said receiving means comprising repeating andamplifying electron tubes in series with said channel, means forseparating said pulsating half-cycle signal currents from voicefrequency currents and an operating device responsive to any polarity ofsaid half-cycle signal currents.

7. In a transmitting system comprising the transmission of pulsatinghalf-cycle direct signal currents of any sequence of polarity and ofabout the same magnitude as that of voice frequency currents to betransmitted over a communication channel, two stations, a direct currentsource at each station, at one station transmitting means connected tothe communication channel and at the other station receiving meansconnected to said channel, said receiving means comprising two push-pullrepeating and amplifying electron tubes connected in series with saidchannel, the plates of said tubes being connected to each end of theprimary of a transformer, the secondary of which is connected parallelto a condenser and to an operating device responsive to any polarity ofsaid half-cycle signal currents.

8. In a transmitting system comprising the transmission of pulsatinghalf-cycle direct signal currents of any sequence of polarity and ofabout the same magnitude as that of voice frequency currents to betransmitted over a communication channel, two stations, a direct currentsource at each station, at one station transmitting means connected tothe communication channel and at the other station receiving meansconnected to said channel, said receiving means comprising two push-pullrepeating and amplifying tubes connected in series with said channel,the plates of said tubes being connected in series with a potentiometer;the center of which is connected to a plate voltage battery source, acondenser connected in parallel to said potentiometer, a third electrontube, the filament and grid of which are connected in series with saidcondenser, the plate and plate battery source of said third amplifierbeing connected in series with the primary of a transformer, and apolarized relay being connected to the secondary of said transformer toreceive the said half-cycle signal currents of any polarity from saidcondenser.

9. In a transmitting system comprising the transmission of pulsatinghalf-cycle direct signal currents of any sequence of polarity, each ofsaid half-cycle currents of about the same duration as a half-cycle ofcurrents within the lower part of the voice frequency range to betransmitted over a communication channel, two stations, a direct currentsource at each station, at one station transmitting means connected tothe transmitting channel and at the other station receiving meansconnected to said channel, said receiving means comprising repeating andamplifying electron tubes in series with said channel, means forseparating said pulsating half-cycle signal currents from voicefrequency currents, and an operating device responsive to any polarityof said half-cycle signal currents.

10. In a transmitting system comprising the transmission of pulsatinghalf-cycle direct signal currents of any sequence of polarity over acommunication carrier channel, two stations each thereof comprising adirect current source, a carrier current generating source, transmittingand receiving means connected to said carrier channel, modulatingfiltering and demodulating means associated with said carrier channel tomodulate and demodulate the said half-cycle signal currents with respectto carrier waves to be transmitted over said channel, said receivingmeans comprising an electron tube amplifier and means for separatingsaid pulsating half-cycle signal currents from any other dampened orcontinuous wave currents to be transmitted over the channel and a deviceresponsiveto any polarity of said half-cycle signal currents.

IQARL HARRY THUNELL. STEN DANIEL VIGREN. PER HARRY ELIAS CLAESSON.

